NEW DELHI, Dec 4 : Oil prices firmed on Thursday after Ukrainian attacks on Russia's oil infrastructure signalled potential supply constraints, and stalled peace talks tempered expectations of a deal restoring Russian oil flows to global markets, though weak fundamentals kept gains limited. Brent crude rose 41 cents, or 0.65 per cent, to $63.08 at 0659 GMT, while U.S. West Texas Intermediate rose 45 cents, or 0.76 per cent, to $59.40. Ukraine hit the Druzhba oil pipeline in Russia's central